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Lost my COM radio mid flight out of Wichita, tracing a chafed wire saved the trip
I was doing a ramp check on a Cessna 172 at a small field in Wichita two weeks ago when the pilot mentioned his COM1 would cut out for a few seconds over the river. I pulled the radio and found the tray pins looked clean, so I grabbed my Fluke and started wiggling the harness while watching the meter. Sure enough, right where the bundle rubbed the airframe former, the insulation was worn down to bare copper on one wire. It took me about 40 minutes to trace it back, splice in a new section, and add a rubber grommet so it wouldn't happen again. Test flight came back with a solid radio the whole way. Has anyone else run into a chafe point that only shows up with vibration on the ground and never in the hangar?
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ryan_ellis20d ago
The part about wiggling the harness while watching the meter is the right move, but one thing to keep in mind: a chafed wire that only acts up with vibration usually won't show a steady short. The copper strands can stay connected most of the time and only break contact for a split second when the bundle flexes, so a Fluke on continuity will just beep and look fine unless you catch it at the exact moment. Better trick is to hook up a meter with a min/max or a cheap tone generator and shake the harness hard while watching for even a tiny blip. If the meter never drops, you got lucky and found it by eye, but the harness could still have a strand break hiding inside the insulation.
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